evaluation of glomerular filtration rate estimating formulas in diabetic patients with chronic kidney disease

objective: measurement of glomerular filtration rate (gfr) is the best determinant in assessment of kidney function for diagnostic and therapeutic purposes. as extremely accurate methods of gfr measurement (i.e. inulin clearance) are expensive and time-consuming and due to limitations of the 24 hour urine collection method, some formula have been developed for the gfr measurement. here we have compared the gfr calculated via cg or mdrd formulas and that measured by creatinine clearance in 24-hour urine collection method in diabetes patients with chronic kidney disease (ckd). materials and methods: this study was performed on 75 diabetes patients with stage 3 or 4 ckd (15-19 ml/min/1.73m2) in the nephrology clinics of the yazd medical university. the gfr was measured via cg and mdrd formula and also via creatinine clearance in 24-hour urine collection method. correlation test and bland altman plot was utilized to check for the relationship between creatinine clearance and the gfr. results: results show a significant correlation of the gfr calculated via creatinine clearance in 24-hour urine collection with gfr calculated via cg (r= 0.75) and with mdrd (r=0.70) formulas. this correlation was even increased when serum levels of creatinine was >1.5 mg/dl or in patients with stage 4 ckd. comparison of the differences between gfr calculated via cg or mdrd formulas and creatinine clearance in 24-hour urine collection method using bland altman showed a lower bias (cg: 17.76 mdrd: 10.64 ml/min/1.73 m2) and narrower limits of agreement (mdrd: -11.33 – 32.62, cg: -4.68 – 40.20) to the creatinine clearance in 24-hour urine collection for the mdrd formula compared to that for the cg formula. conclusion: cg and mdrd correlate well with creatinine clearance in 24-hour urine collection, while mdrd is more accurate in diabetes patients with stage 3 or 4 ckd.